JP7175586B2 - Boron nitride particle aggregate, method for producing the same, composition, and resin sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a boron nitride particle aggregate, a method for producing the same, a composition, and a resin sheet.

2. Description of the Related Art In recent years, the density of heat generation inside electronic equipment is increasing year by year as the circuits of electric equipment or electronic equipment become faster and more highly integrated, and the mounting density of heat-generating electronic components on printed wiring boards increases. Therefore, there is a demand for a member having high thermal conductivity and electrical insulation that efficiently dissipates heat generated by electronic components and the like.

Boron nitride particles having a hexagonal crystal structure are relatively easy to synthesize and have excellent thermal conductivity, solid lubricity, chemical stability, and heat resistance. Fillers for thermally conductive rubber, heat-dissipating grease, heat-dissipating sealant, semiconductor encapsulation resin, mold release agent for molten metal and glass, solid lubricant, raw material for cosmetics, etc. It's being used.

In recent years, in high-performance electronic equipment, the amount of heat generated by various electronic components has increased due to higher integration, higher speed, smaller size, and lighter weight. There is a need for thermally conductive sheets that are electrically conductive. Therefore, various thermally conductive sheets have been proposed in which boron nitride, which is excellent in thermal conductivity and electrical insulation, is dispersed as a thermally conductive filler in an organic matrix material.

Boron nitride particles are generally scale-like due to their hexagonal crystal form, and are known to have directional anisotropy in thermal conductivity. Ordinary scaly boron nitride particles have higher thermal conductivity in the plane direction (a-axis direction) than in the thickness direction (c-axis direction). In the thermally conductive sheet containing such scaly boron nitride particles, the c-axis direction of the boron nitride particles tends to be oriented in the thickness direction of the insulating heat-dissipating sheet. There is a problem that thermal conductivity in the thickness direction is inferior.

For example, Patent Document 1 proposes a boron nitride particle aggregate in which primary particles of boron nitride are randomly aggregated in order to improve the thermal anisotropy of such boron nitride particles.

Further, Patent Document 2 proposes a boron nitride particle aggregate in which primary particles of boron nitride are radially aggregated.

Furthermore, Patent Document 3 proposes a boron nitride particle aggregate in which primary particles of boron nitride to which a silane coupling agent having a vinyl group is added are aggregated so as to be randomly oriented.

JP-A-9-202663 JP-A-2015-6980 JP 2012-56818 A

Since the aggregated boron nitride particles described in Patent Documents 1 to 3 are aggregates (secondary particles) in which the primary particles of boron nitride are randomly aggregated, such as when kneading with the resin, during the production process of the resin sheet, the Secondary particles may collapse, and there is still room for improvement in terms of thermal conductivity in the thickness direction of the resin sheet.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel boron nitride particle agglomerate capable of improving the thermal conductivity in the thickness direction of a resin sheet.

The present inventors have made intensive studies to solve the above problems. As a result, the inventors have found that the above object can be achieved by a novel boron nitride particle agglomerate in which the (0001) planes of the primary particles of boron nitride overlap and agglomerate, and have completed the present invention.

That is, the present invention is as follows.
<1>
A boron nitride particle aggregate containing hexagonal boron nitride primary particles,
A boron nitride particle aggregate in which the (0001) planes of the hexagonal boron nitride primary particles overlap each other.
<2>
The boron nitride particle aggregate according to <1>, which has a columnar shape.
<3>
<1> or <2>, wherein the relationship between the longest diameter R in the stacking direction of the boron nitride particle aggregates and the longest diameter r in the width direction of the boron nitride particle aggregates is represented by the following formula (1): Boron nitride particle agglomerates according to .
0.3r<R (1)
<4>
A method for producing a boron nitride particle aggregate according to any one of <1> to <3>,
a step (A) of adding a coupling agent to the hexagonal boron nitride primary particles;
a step (B) of dispersing the coupling agent-added primary particles of hexagonal boron nitride obtained in the step (A) in a solvent;
A method for producing a boron nitride particle aggregate, comprising:
<5>
The method for producing boron nitride particle aggregates according to <4>, wherein the coupling agent has at least one selected from the group consisting of aryl groups, amino groups, epoxy groups, cyanate groups, mercapto groups and halogens.
<6>
The method for producing a boron nitride particle aggregate according to <4> or <4>, wherein the coupling agent contains a silane coupling agent having a crosslinked structure or a silane coupling agent having an aryl group.
<7>
A composition comprising a filler containing the boron nitride particle aggregate according to any one of <1> to <3>, and a resin.
<8>
The composition according to <7>, wherein the resin is a thermosetting resin.
<9>
A resin sheet comprising the composition according to <7> or <8> and a support.
<10>
The resin sheet according to <9>, wherein the intensity ratio between the <002> X-ray diffraction intensity and the <100> X-ray diffraction intensity (I<002>/I<100>) is 30 or less.

According to the present invention, it is possible to provide a novel boron nitride particle aggregate that improves the thermal conductivity in the thickness direction when made into a resin sheet.

FIG. 1 is an explanatory diagram for explaining R and r in this embodiment. FIG. 2(a) is an SEM image of the boron nitride particle aggregate according to Example 1 at a magnification of 120000 times. FIG. 2(b) is an SEM image of the boron nitride particle aggregate according to Example 1 at a magnification of 50000 times. FIG. 3(a) is an SEM image at a magnification of 25000 times of conventional hexagonal boron nitride primary particles in which the hexagonal boron nitride primary particles are not agglomerated. FIG. 3(b) shows an SEM image of hexagonal boron nitride primary particles in which the hexagonal boron nitride primary particles are not agglomerated, and shows a portion where the end face side is observed. FIG. 4 is an SEM image at 1000× magnification of conventional boron nitride particle agglomerates that are randomly agglomerated. FIG. 5 is a diagram showing the scale of the boron nitride particle aggregates observed in FIG. 2(a). FIG. 6 is a diagram to illustrate the scale of the three boron nitride particle aggregates observed in FIG. 2(b).

An embodiment of the present invention (hereinafter referred to as "this embodiment") will be described below. In addition, this embodiment is an illustration for demonstrating this invention, and this invention is not limited only to this embodiment.

(Boron nitride particle aggregate)
The boron nitride particle aggregate of the present embodiment is a boron nitride particle aggregate containing hexagonal boron nitride primary particles, and the (0001) planes of the hexagonal boron nitride primary particles overlap each other. Since it is configured in this way, the boron nitride particle aggregate of the present embodiment can improve the thermal conductivity in the thickness direction of the resin sheet when formed into a resin sheet. Details of the resin sheet will be described later.

The particle shape of the hexagonal boron nitride primary particles in the present embodiment is not particularly limited, but examples thereof include scaly, flattened, granular, spherical, fibrous, and whisker-like, with scaly being preferred.

The average particle diameter of the hexagonal boron nitride primary particles is not particularly limited, but the median diameter is preferably 0.1 to 50 μm, more preferably 0.1 to 5 μm, and particularly preferably 0.1 to 1 μm. When the average particle size is within the above range, the (0001) planes of the hexagonal boron nitride primary particles are likely to overlap and agglomerate, and as a result, the thermal conductivity in the thickness direction of the resin sheet tends to improve.
Here, the average particle diameter of the hexagonal boron nitride primary particles can be measured, for example, by a wet laser diffraction/scattering method.

The aggregation form of the boron nitride particle aggregates in which the (0001) planes of the hexagonal boron nitride primary particles are overlapped and aggregated is not particularly limited, but natural aggregation, aggregation by an aggregating agent, physical aggregation, and the like are possible. mentioned. Examples of spontaneous aggregation include, but are not limited to, aggregation caused by Van der Waals force, electrostatic force, adsorbed moisture, and the like. Aggregation by aggregating agents includes, but is not limited to, aggregation by aggregating agents such as coupling agents, inorganic salts, and polymeric substances. For example, when a coupling agent is used as an aggregating agent, it is preferable to agglomerate by changing the surface state of the primary particles of hexagonal boron nitride to a state of high surface energy, that is, a state of facilitating agglomeration. Physical agglomeration includes a method of aggregating by operations such as mixing granulation, extrusion granulation, and spray drying. Among them, aggregation by a coupling agent is preferable from the viewpoint of cohesive force.

As used herein, the term “boron nitride particle aggregate” refers to aggregate units of secondary particles formed by agglomeration of inorganic fillers containing hexagonal boron nitride primary particles, and can take various forms. That is, the shape of the boron nitride particle aggregate is not particularly limited as long as the (0001) planes of the hexagonal boron nitride primary particles are overlapped with each other and aggregated. It may be spherical, fibrous, or the like.

In the present embodiment, when the boron nitride particle aggregate has a columnar shape, when it is made into a resin sheet, the a-axis direction of the hexagonal boron nitride primary particles may coincide with the thickness direction of the resin sheet (hereinafter, simply Also referred to as “orientation”) tends to increase, which is preferable. As used herein, the term “columnar” refers to a shape derived from the aggregation mode of the hexagonal boron nitride primary particles, and includes prismatic, cylindrical, rod-like, etc. shapes, which are different from spherical. . Furthermore, the columnar shape includes those that extend straight in the vertical direction, those that extend in a slanted shape, those that extend while curving, those that extend in a branched shape, and the like. It can be easily confirmed by scanning electron microscope (SEM) observation that the boron nitride particle aggregates have a columnar shape.

Typical examples of methods for confirming that the boron nitride particle aggregates of the present embodiment have a columnar shape include, but are not limited to, the longest diameter R in the stacking direction of the boron nitride particle aggregates, and the boron nitride particle aggregates and the longest diameter r in the width direction are specified by SEM observation, and the magnitude relationship between them is confirmed. In addition, in the present embodiment, the boron nitride particle aggregate preferably satisfies R>0.3r from the viewpoint of further increasing the orientation. Moreover, in the present embodiment, it is more preferable to satisfy R>r from the viewpoint of further increasing the orientation. The "stacking direction" as used herein is a direction substantially parallel to the c-axis direction of the hexagonal boron nitride primary particles. Also, the "width direction" is a direction substantially perpendicular to the stacking direction. In other words, the width direction is a direction substantially parallel to the plane direction (a-axis direction) of the (0001) plane in at least one hexagonal boron nitride primary particle. In the present embodiment, the longest diameter in the width direction is, for example, when the boron nitride particle aggregate has a columnar shape extending straight in the vertical direction, the longest diameter in the plane direction of the (0001) plane of the hexagonal boron nitride primary particles However, it is not limited to such a relationship, and the longest diameter in the width direction can take a value larger than the longest diameter in the plane direction of the (0001) plane of the hexagonal boron nitride primary particles. Here, “substantially parallel” means a state within ±10° from the parallel direction, and “substantially perpendicular” means a state within ±10° from the vertical direction.
R and r will be specifically described with reference to FIG. The hexagonal boron nitride primary particles exemplified in FIG. 1(a) are shown as a two-dimensional rectangle as a typical example, and the long side (r) corresponds to the (0001) plane. , the short side (R) corresponds to the end face. The boron nitride particle aggregate exemplified in FIG. 1(b) is obtained by aggregating rectangular hexagonal boron nitride primary particles so that their long sides, that is, (0001) plane sides overlap each other. The short side of this aggregate corresponds to r (that is, the longest diameter in the width direction of the boron nitride particle aggregate), and the long side corresponds to R (that is, the longest diameter in the stacking direction of the boron nitride particle aggregate). is doing.

As described above, the boron nitride particle aggregate of the present embodiment has a structure in which hexagonal boron nitride primary particles are laminated, and the laminated structure is not particularly limited, but the hexagonal boron nitride primary per layer The number of particles in the particles is preferably 2 or less, more preferably 1. Having such a laminated structure is preferable because the orientation tends to increase.

As described above, the longest diameter in the stacking direction of the boron nitride particle aggregates is not particularly limited, and the longest diameter in the width direction of the boron nitride particle aggregates is not particularly limited either. In this embodiment, when the average particle size of the hexagonal boron nitride primary particles is A (μm), R = 0.3 × A to 10 × A (μm) and r = 0.3 × A to 3 × A (μm) is preferably satisfied. Specifically, taking the case where the average particle diameter of the hexagonal boron nitride primary particles is 0.5 μm as an example, it is typical to take a value of about R = 0.15 to 5 μm, and r = 0.15. Values of the order of ˜1.5 μm are typical. Specific examples of the method for measuring the longest diameter include, but are not limited to, the following, but in the photographed SEM image, if the boron nitride particle aggregate is columnar, the shape is approximated to a rectangle, and the long side and For example, the length of the short side is measured.

In the present embodiment, as long as the hexagonal boron nitride primary particles are stacked so as to form a columnar shape as the aggregate of the hexagonal boron nitride particles, "the (0001) planes of the hexagonal boron nitride primary particles overlap". The state in which they are present is not limited to the mode in which they overlap completely, but also includes the mode in which they overlap in the width direction.

In addition, the longest diameter r in the width direction of the boron nitride particle aggregates tends to depend on the particle size and degree of aggregation of the hexagonal boron nitride primary particles, and is not particularly limited. Preferably, the thickness of the molding is less than T (r<T), more preferably r<0.9*T, even more preferably r<0.5*T. When the above range is satisfied, there is a tendency to prevent a decrease in smoothness due to unevenness on the surface of the molded product, and from the viewpoint that it can be used as a raw material for a thinner resin sheet, r should be sufficiently smaller than T. is preferred.

The boron nitride particle aggregate of the present embodiment may contain an inorganic filler other than the hexagonal boron nitride primary particles. Examples of such inorganic fillers include, but are not limited to, aluminum nitride, aluminum oxide, Metals and alloys such as metal oxides such as zinc oxide, silicon carbide and aluminum hydroxide, metal nitrides, metal carbides and metal hydroxides, spherical, powdery, fibrous, needle-like, carbon, graphite and diamond Scale-like and whisker-like fillers are included. These may be contained independently and may contain multiple types.

The boron nitride particle aggregate of the present embodiment may contain a binder from the viewpoint of increasing the toughness of the boron nitride particle aggregate. The term “robustness” as used herein is a property indicating the strength of bonding when the primary hexagonal boron particles in this embodiment are bonded together. Binders originally act to firmly bind primary particles together and stabilize the shape of aggregates.

Metal oxides are preferred as such binders, and specifically, aluminum oxide, magnesium oxide, yttrium oxide, calcium oxide, silicon oxide, boron oxide, cerium oxide, zirconium oxide, titanium oxide, and the like are preferably used. Among these, aluminum oxide and yttrium oxide are preferable from the viewpoint of thermal conductivity and heat resistance as oxides, and bonding strength for bonding primary particles of hexagonal boron nitride. The binder may be a liquid binder such as alumina sol, or may be an organometallic compound that is converted to a metal oxide by firing. These binders may be used individually by 1 type, and may mix 2 or more types.

(Method for producing boron nitride particle aggregate)
The boron nitride particle aggregate of the present embodiment is not particularly limited as long as the above-described structure can be obtained, but is preferably produced by the following method. That is, the preferred method for producing a boron nitride particle aggregate in the present embodiment includes the step (A) of adding a coupling agent to the hexagonal boron nitride primary particles, and the coupling agent obtained in the step (A). and a step (B) of dispersing the boron nitride primary particles in a solvent. Moreover, it is more preferable to further include the step (C) of separating the boron nitride particle aggregates from the dispersion liquid obtained in the step (B).
When the step (A) and the step (B) are included, the hexagonal boron nitride primary particles to which the coupling agent is added are aggregated between the (0001) planes due to the surface charge in the dispersion, and a binding phase is formed between the coupling agents. and is preferable because it facilitates obtaining the boron nitride particle aggregate having the desired configuration of the present embodiment.

In the step (A), the method of adding the coupling agent to the hexagonal boron nitride primary particles is not particularly limited. A dry method of treatment and a wet method of immersing primary particles of hexagonal boron nitride in a dilute solution of a coupling agent and stirring are suitable.
In the stage of step (A), the primary particles of hexagonal boron nitride to which the coupling agent is added are sometimes bonded to form a boron nitride particle agglomerate. The stirring temperature is not particularly limited, but no special temperature control such as heating or cooling is required. The temperature is usually raised by stirring, but it is preferably 200° C. or less. The stirring speed is also not particularly limited, but it is usually preferably stirred at 10 to 10,000 rpm, more preferably 100 to 3,000 rpm. The stirring time is preferably 5 minutes to 180 minutes, more preferably 10 minutes to 60 minutes from the viewpoint of effective stirring time and productivity.

From the viewpoint of cohesive strength and toughness, the above coupling agent preferably contains at least one selected from the group consisting of aryl groups, amino groups, epoxy groups, cyanate groups, mercapto groups and halogens. Examples of such coupling agents include, but are not limited to, silane-based, titanate-based, zirconate-based, zirconium aluminate-based, and aluminate-based coupling agents. Among them, a silane-based coupling agent (hereinafter also referred to as "silane coupling agent") is preferable from the viewpoint of cohesion.

The silane coupling agent described above preferably contains at least one selected from the group consisting of aryl groups, amino groups, epoxy groups, cyanate groups, mercapto groups and halogens. Among them, it is more preferable to have an aryl group because it has a π-π bond and the bond between the silane coupling agents becomes stronger. Examples of such coupling agents include, but are not limited to, phenyltrimethoxysilane, phenyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, p-styryltrimethoxysilane, naphthyltrimethoxysilane. , naphthyltriethoxysilane, (trimethoxysilyl)anthracene, (triethoxysilyl)anthracene, and the like.

It is also preferable to use a silane coupling agent having a crosslinked structure as the above coupling agent. Specific examples of such silane coupling agents include, but are not limited to, 1,6-bis(trimethoxysilyl)hexane, tris-(trimethoxysilylpropyl)isocyanurate, bis(triethoxysilylpropyl)tetra sulfide, hexamethyldisilazane, and the like.

The silane coupling agent having the crosslinked structure described above can also be obtained by reacting organic functional groups to crosslink. Combinations of organic functional groups in this case are not limited to the following, but examples include amino group-epoxy group, epoxy group-cyanate group, amino group-cyanate group, amino group-sulfonic acid group, amino group-halogen, mercapto Group-organic functional group combinations of coupling agents such as cyanate groups may be mentioned.

The various coupling agents described above may be used singly or in combination of two or more.

The amount of the coupling agent added in the step (A) is 0.01 to 10 times the surface area of the hexagonal boron nitride primary particles, depending on the surface area of the inorganic filler, that is, the surface area of the hexagonal boron nitride primary particles. It is preferable to add 1% by mass, more preferably 1 to 2% by mass.

In the production method of the present embodiment, the stirring method that can be used when adding the coupling agent is not particularly limited. Stirring can be performed using a general stirrer such as a mixer.

In step (B), the primary particles of hexagonal boron nitride added with the coupling agent obtained in step (A) are dispersed in a solvent. The method of dispersing the hexagonal boron nitride primary particles to which the coupling agent is added in the solvent is not particularly limited. Since the (0001) planes of hexagonal boron nitride primary particles to which a coupling agent having an aromatic skeleton is added tend to agglomerate, it is preferable to ultrasonically disperse them in a solvent.

The solvent used in step (B) is not particularly limited, and water and/or various organic solvents can be used. When using hexagonal boron nitride primary particles having an aromatic ring skeleton, that is, to which a coupling agent having an aryl group is added, a highly polar solvent is preferred.
The amount of the solvent used is 0.5 to 20 times the mass of the hexagonal boron nitride primary particles, from the viewpoint of reducing the load during separation in step (C) and from the viewpoint of uniform dispersion in step (B). preferably.

In step (B), various surfactants may be added from the viewpoint of adjusting the degree of aggregation of the boron nitride particle aggregates. The surfactant is not particularly limited, and for example, anionic surfactants, cationic surfactants, nonionic surfactants, etc. can be used, and these may be used alone. , may be used in combination of two or more. The surfactant concentration in the dispersion obtained in step (B) is not particularly limited, but it can be usually 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less. preferably.

In step (C), boron nitride particle aggregates are separated from the dispersion liquid obtained in step (B). The method for separating the boron nitride particle aggregates from the dispersion liquid obtained in step (B) is not particularly limited, and for example, static separation, filtration, centrifugation, heat treatment, etc. can be used.

The boron nitride particle agglomerate thus obtained may be subjected to further treatment. For example, surface oxidation by temperature treatment under oxygen, water vapor treatment, surface modification with organometallic compounds or polymers using carrier or reaction gas at room temperature or under heating, sol-gel method using boehmite or SiO ₂ , etc. can be used. is. These treatments may be used singly or in combination of two or more.

Further, the boron nitride particle agglomerates of the present embodiment produced as described above may be subjected to typical post-processes such as scrutinization, pulverization, classification, purification, washing and drying, if necessary. If fines are present, they may be removed first. As an alternative to sieving, said comminution of the boron nitride particle agglomerates may be carried out using sieve screens, classification mills, structured roller crushers or cutting wheels. For example, dry milling in a ball mill is also possible.

Although the use of the boron nitride particle aggregate of the present embodiment is not particularly limited, it is preferably used as a composition containing a filler containing the boron nitride particle aggregate and a resin. That is, the composition of the present embodiment contains a filler containing the boron nitride particle aggregate of the present embodiment and a resin. As described above, the composition obtained by filling the boron nitride particle aggregate of the present embodiment has low anisotropy in thermal conductivity, has high thermal conductivity, and has low entrainment of air bubbles. Indicates insulation resistance. Furthermore, even if the resin is highly filled, an increase in viscosity during kneading can be suppressed, and excellent moldability can be exhibited. The filler in the present embodiment may contain an inorganic filler other than the boron nitride particle aggregates. Examples of such inorganic fillers include, but are not limited to, aluminum nitride, aluminum oxide, zinc oxide, Metal oxides such as silicon carbide and aluminum hydroxide, metals and alloys such as metal nitrides, metal carbides and metal hydroxides, spherical, powdery, fibrous, needle-like, scaly, Fillers such as whisker-like fillers are included. These may be contained independently and may contain multiple types.
Examples of the above resin include, but are not limited to, thermoplastic resins (polyolefin, vinyl chloride resin, methyl methacrylate resin, nylon, fluororesin), thermosetting resins (epoxy resin, phenolic resin, urea resin, melamine resins, unsaturated polyester resins, silicone resins), synthetic rubbers, liquid gels, and the like. Among the above, thermosetting resins are preferred.
The method for producing the composition of the present embodiment is not particularly limited, but an example thereof includes a method of sequentially blending each component in a solvent and sufficiently stirring the mixture. At this time, in order to uniformly dissolve or disperse each component, known treatments such as stirring, mixing and kneading treatment can be performed. Specifically, the dispersibility of the filler such as boron nitride particle aggregates in the composition can be improved by performing the stirring and dispersing treatment using a stirring tank equipped with a stirrer having an appropriate stirring ability. The above stirring, mixing, and kneading treatments can be appropriately performed using, for example, a device for mixing purposes such as a ball mill or bead mill, or a known device such as a revolution or rotation type mixing device.
In addition, an organic solvent can be used as necessary during the preparation of the composition of the present embodiment. The type of organic solvent is not particularly limited as long as it can dissolve part or all of the resin components in the composition. Examples include ketones such as acetone, methyl ethyl ketone, methyl cellosolve, and cyclohexanone; amides such as dimethylformamide; propylene glycol monomethyl ether and acetate thereof; A solvent may be used individually by 1 type, or may use 2 or more types together.

Furthermore, it is preferably used as a resin sheet containing the composition described above and a support. That is, the resin sheet of this embodiment includes the composition of this embodiment and a support. The resin sheet of the present embodiment is used as one means of thinning, and can be produced, for example, by directly coating and drying the composition on a support such as a metal foil or film.
The support in the present embodiment is not particularly limited, but known materials used for various printed wiring board materials can be used. Specific examples of the support include polyimide film, polyamide film, polyester film, polyethylene terephthalate (PET) film, polybutylene terephthalate (PBT) film, polypropylene (PP) film, polyethylene (PE) film, aluminum foil, copper foil, Examples include gold leaf. Among them, electrolytic copper foil and PET film are preferable.
Examples of the coating method include a method in which a solution obtained by dissolving the composition of the present embodiment in a solvent is coated on the support using a bar coater, die coater, doctor blade, baker applicator, or the like.
The resin sheet is preferably obtained by applying the composition of the present embodiment to a support and then semi-curing it (bringing it to a B-stage). Specifically, for example, the above composition is applied to a support such as a copper foil, and then semi-cured by heating in a dryer at 100 to 200° C. for 1 to 60 minutes to produce a resin sheet. methods and the like. The amount of the resin composition adhered to the support is preferably in the range of 1 to 1000 μm in terms of resin thickness of the resin sheet.

The resin sheet preferably has an intensity ratio (I<002>/I<100>) between <002> X-ray diffraction intensity and <100> X-ray diffraction intensity of 30 or less. Here, the intensity ratio between the intensity of <002> X-ray diffraction and the intensity of <100> X-ray diffraction (I<002>/I<100>) is the X-ray in the thickness direction of the sheet of the resin composition. , that is, the peak intensity ratio of the <002> diffraction line and the <100> diffraction line obtained by irradiation at an angle of 90° with respect to the length direction of the sheet (I<002>/I< 100>). In the present embodiment, the fact that the strength ratio is 30 or less suggests that the orientation is sufficiently high, and the thermal conductivity in the sheet thickness direction tends to be higher.

The boron nitride particle agglomerates of the present embodiments may also be used for other applications, such as for making sintered bodies.
Specifically, it can be used for various uses known as uses of boron nitride particles. An example of a particularly suitable application is as a filler for resins intended to improve electrical insulation or impart thermal conductivity by being filled in resins.

Other uses include raw materials for processed hexagonal boron nitride products such as cubic boron nitride and hexagonal boron nitride molded products, nucleating agents for engineering plastics, phase change materials, solid or liquid thermal interface materials, melting Release agents for metal and molten glass molds, cosmetics, raw materials for composite ceramics, and the like.

Next, the present embodiment will be described in more detail with reference to examples, but the present embodiment is not limited by these examples.

<Evaluation method for each characteristic>
(1) Thermal conductivity A test piece (10 mm x 10 mm x 1 mm thick) was cut out from a press-molded sheet to be described later. Using a NETZSCH xenon flash analyzer model LFA447 thermal conductivity meter, the thermal conductivity in the sheet thickness direction was measured with a laser flash on this test piece.
(2) Orientation intensity ratio The orientation of the hexagonal boron nitride primary particles in the composite sheet is determined by the intensity of the I (002) diffraction line (2θ = 26.5 °) and the I (100) diffraction by the X-ray diffraction method. It was evaluated by the ratio (I(002)/I(100)) to the intensity of the line (2θ=41.5°).
The thickness direction of the hexagonal boron nitride primary particles coincides with the crystallographic I (002) diffraction line, that is, the c-axis direction, and the in-plane direction coincides with the I (100) diffraction line, that is, the a-axis direction. there is When the hexagonal boron nitride primary particles that make up the boron nitride particle aggregates are completely randomly oriented (non-oriented), (I (002) / I (100)) ≈ 6.7 ("JCPDS [ Powder X-ray diffraction database]” Crystal density value [Dx] of No. 34-0421 [BN]). When (I(002)/I(100)) is small, the a-axis direction of the hexagonal boron nitride particles is oriented in the thickness direction of the composite sheet. Conductivity increases.
In the above-described measurement, a composite sheet of 5 mm×5 mm×0.2 mm in thickness was cut out from a press-molded sheet to be described later and used as a measurement sample. In addition, a plane of 5 mm×5 mm of the composite sheet was irradiated with X-rays in the thickness direction of the composite sheet using a “fully automatic horizontal multipurpose X-ray diffraction device SmartLab” (manufactured by Rigaku Corporation). During the measurement, CuKα rays were used as the X-ray source, the tube voltage was 45 kV, and the tube current was 360 mA.

(Example 1)
1.5% by mass of phenyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) as a coupling agent is added dropwise to hexagonal boron nitride primary particles (manufactured by Showa Denko "UHP-S2") having an average particle diameter of 0.5 μm, and a mixer is added. to obtain hexagonal boron nitride primary particles to which a coupling agent was added. Subsequently, primary particles of hexagonal boron nitride obtained by adding the above coupling agent to methyl ethyl ketone were added and sufficiently dispersed by an ultrasonic disperser to obtain a dispersion liquid. This dispersion was allowed to stand for 6 hours, and the supernatant was removed to obtain a boron nitride particle aggregate. This boron nitride particle aggregate was further ultrasonically dispersed in ethanol, spread on aluminum foil, and after the solvent was evaporated, was pressed against a carbon tape, and an SEM image of the boron nitride particle aggregate was observed. The results are shown in FIGS. 2(a) and 2(b).

In the SEM images shown in FIGS. 2(a) and 2(b), the end faces of the hexagonal boron nitride primary particles are observed more than the (0001) planes of the hexagonal boron nitride primary particles, and most of the boron nitride It was found that the primary particles were aggregated with overlapping (0001) planes. That is, many boron nitride particles (boron nitride particle aggregates) in which the (0001) planes of boron nitride primary particles overlap and aggregate were observed. Regarding the boron nitride particle aggregate shown in FIG. 2( a ), the number of particles of hexagonal boron nitride primary particles per layer is 1, and the longest diameter R in the stacking direction of this boron nitride particle aggregate and the boron nitride particles When the longest diameter r in the width direction of the aggregate was measured, it was found to be R=0.66 μm, r=0.49 μm, and R/r=1.35. Note that R is specified as shown in FIG. In addition, three boron nitride particle aggregates (boron nitride particle aggregates 1 to 3) having a particularly typical columnar shape are selected from FIG. 2(b), and the particle size is measured by the method described later. did. In all of the boron nitride particle aggregates 1 to 3, the number of hexagonal boron nitride primary particles per layer was one. This boron nitride particle aggregate was charged and the SEM image was distorted. Table 1 shows the results of determining r and R for the boron nitride particle aggregates 1 to 3. These R's are specified as shown in FIG.

(Measurement of particle size)
The morphology of the boron nitride particle aggregates was analyzed by an electron microscope (FE-SEM-EDX (SU8220): manufactured by Hitachi High Technology Co., Ltd.) on a plurality of SEM observation images of 2.5 μm×1.8 μm squares. R and r were measured for boron nitride particles (boron nitride particle aggregates) in which the (0001) planes of the boron nitride primary particles overlapped and aggregated in the observation range. At that time, the boron nitride particles observed in the SEM image were approximated to a rectangle as shown in FIG. 1(b), and the length of the side corresponding to R and the length of the side corresponding to r were measured.

(Comparative example 1)
Boron nitride particles of Comparative Example 1 were obtained in the same manner as in Example 1, except that the hexagonal boron nitride primary particles were not surface-treated with a coupling agent. A SEM observation image of the obtained boron nitride particles is shown in FIG.

As can be seen from FIG. 3(a), it was observed that the (0001) planes of many hexagonal boron nitride primary particles faced the upper surface of the sample. That is, no structure in which (0001) hexagonal boron nitride primary particles overlapped with each other was observed. Moreover, as shown in FIG. 3(b), some of the hexagonal boron nitride primary particles were observed to have the plane direction of the end face aligned with the thickness direction of the sample. The boron nitride particles observed in these SEM images were approximated to a rectangle as shown in FIG. 1(a), and the length of the side corresponding to R and the length of the side corresponding to r were measured. The longest diameter r′ in the width direction of the hexagonal boron nitride primary particles is 0.3 to 1.0 μm, and the longest diameter R′ in the direction perpendicular to the width direction of the hexagonal boron nitride primary particles is 0.01. ~0.05 μm. That is, all observed hexagonal boron nitride primary particles had R'<0.3r'.

(Comparative example 2)
A boron nitride particle aggregate of Comparative Example 2 was obtained in the same manner as in Example 1 except that a commercially available boron nitride particle random aggregate (“SGPS” manufactured by Denki Kagaku Kogyo Co., Ltd.) was used. A SEM observation image of the obtained boron nitride particle aggregate is shown in FIG. As can be seen from FIG. 4, the hexagonal boron nitride primary particles were observed to have a randomly aggregated structure. That is, no structure in which (0001) hexagonal boron nitride primary particles overlapped with each other was observed. In the obtained random aggregates, the number of hexagonal boron nitride primary particles per layer was 3 or more, and the shape of the random aggregates was spherical.

As shown in FIG. 2, it was confirmed that by using the production method of the present embodiment, a boron nitride particle agglomerate in which the (0001) planes of boron nitride particles overlap and agglomerate can be realized.

Next, the boron nitride particle aggregate ((0001) area layer type) of Example 1, the hexagonal boron nitride primary particles of Comparative Example 1, and the boron nitride particle aggregate (random aggregate) of Comparative Example 2 were used as fillers. A composite sheet with a resin was produced by using the resin.
As the resin (base resin), epoxy resin ("EPPN-501H" manufactured by Nippon Kayaku) 100 parts by weight and a curing agent (phenol novolac curing agent, "DL-92" manufactured by Meiwa Kasei) 63 parts by weight, a curing catalyst (2-Phenylimidazole, manufactured by Shikoku Kasei Co., Ltd.) was used as a mixture with 0.1 part by mass.
Next, 40% by volume of each base resin and 60% by volume of the filler of Example 1, Comparative Example 1 or Comparative Example 2 were mixed using methyl ethyl ketone as a solvent, and then this mixed solution was applied to a copper foil, A semi-cured sheet was produced by drying at 130°C. This was cured using a vacuum press under conditions of 180° C. and 10 MPa to produce a composite sheet.

Table 2 shows the results of measurement of the thermal conductivity of the composite sheets of Example 1, Comparative Examples 1 and 2 and the orientation intensity ratio of the hexagonal boron nitride primary particles in the composite sheets.

Claims (8)

A boron nitride particle aggregate containing hexagonal boron nitride primary particles,
The (0001) planes of the hexagonal boron nitride primary particles overlap each other,
The number of particles of the hexagonal boron nitride primary particles per layer of the boron nitride particle aggregate is 2 or less,
having a columnar shape,
A boron nitride particle aggregate, wherein the relationship between the longest diameter R in the stacking direction of the boron nitride particle aggregate and the longest diameter r in the width direction of the boron nitride particle aggregate is represented by the following formula (1).
r<R (1) A method for producing a boron nitride particle aggregate according to claim 1,
a step (A) of adding a coupling agent to the hexagonal boron nitride primary particles;
a step (B) of dispersing the coupling agent-added primary particles of hexagonal boron nitride obtained in the step (A) in a solvent;
A method for producing a boron nitride particle aggregate, comprising: 3. The method for producing boron nitride particle aggregates according to claim 2, wherein the coupling agent has at least one selected from the group consisting of aryl groups, amino groups, epoxy groups, cyanate groups, mercapto groups and halogens. The method for producing a boron nitride particle aggregate according to claim 3, wherein the coupling agent contains a silane coupling agent having a crosslinked structure or a silane coupling agent having an aryl group. A composition comprising a filler comprising the boron nitride particle aggregates of claim 1 and a resin. 6. The composition of claim 5, wherein said resin is a thermosetting resin. A resin sheet comprising the composition according to claim 5 or 6 and a support. 8. The resin sheet according to claim 7, wherein an intensity ratio (I<002>/I<100>) between the intensity of <002> X-ray diffraction and the intensity of <100> X-ray diffraction is 30 or less.

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